Roll of bags and method and device for producing the same

ABSTRACT

Method and device for producing rolls ( 17 ) of bags. At least one longitudinal side edge ( 15, 16 ) of a line of overlapping bags ( 17 ) is folded towards the centre axis of said line of bags. The line is then winded to rolls ( 17 ).

TECHNICAL FIELD

The invention relates to a method and a device for producing plasticbags from a flattened flexible hose. The invention also relates to aroll of plastic bags.

PRIOR ART

It is common practice to produce plastic bags from flexible plastichoses. The hose is flattened and formed into bags that are connected topto bottom by a perforation. Each bag normally extends over the completewidth of the hose. A line of perforated but connected bag are thennormally winded to form a roll of bags, and the roll is then disposed ina paper box or dispenser.

When a bag is to be removed from the roll and used it is necessary tolocate the position of the perforated section and then tear off the bag.Different types of boxes and dispensers have been suggested but manyconsumers still find it difficult or troublesome to tear of the bag inan appropriate way. In prior art there are also rolls off plastic bagsthat are loosely collected in an overlapping position. However, rolls ofthis structure are less stable than rolls of bags that are connected byperforated sections.

SUMMARY OF THE INVENTION

An object of the invention is to improve the production of bags,preferably plastic bags. According to an embodiment of the invention itis possible to produce a roll of bags from which bags can be withdrawnin a simplified way.

Further advantages and features of the invention are shown in thedescription below and in the accompanying drawings and dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toembodiments of the invention shown in the drawings, in which

FIG. 1 is a general plan view of a device for producing bag according toone embodiment of the invention,

FIG. 2 is a side elevation view of the embodiment shown in FIG. 1,

FIG. 3 is a more detailed plan view of the embodiment shown in FIG. 1,

FIG. 4 is a cut out sectional view from A—A in FIG. 2,

FIG. 5 is a sectional view from B—B in FIG. 3,

FIG. 6 is a schematic perspective view of a roll of bags producedaccording to the invention, and

FIG. 7 shows forces exerted on a roll of bags in a box.

DETAILED DESCRIPTION

In FIG. 1 a continuous flattened flexible hose 10 is fed in thedirection of arrow A. The hose is cut into two longitudinally extendingsections by a cutting means 19. Both sections are then cut of from thecontinuous hose into elements 11, 12 by a heating means 23, see FIG. 2.Each element 11, 12 forms a bag when the cut of side edges thereof aresealed by the heating means 23. The heating means cuts and sealstransversely across the hose. Opposite side edges of the elements 11, 12form the openings of the bags.

Each of the bags or elements 11, 12 is supplied to a line 14, 18 on aconveyer fed in the transverse direction of the feeding direction of thehose 10. A cut of bag 11 is disposed on top of a bag 13 already disposedin the line 14.

Side edges 15, 16 of the overlapping bags are folded towards the centreof the line 14 by folding means, see FIG. 3 and FIG. 5, respectively.Rolls 17 of bags only are then formed from the line 14 and disposedautomatically in boxes.

As shown in FIG. 2 the continuous flattened flexible hose 10 is fedbetween a first conveyer 22 and a first and second clamp rollers 20, 21,respectively. The cutting means 19 comprises in a preferred embodiment arazor blade. The heating means 23 is provided between first and secondclamp rollers 20, 21. In one embodiment the heating means 23 is providedon a rotating axis 24 and comprises two opposite radially extendingheating plates. The axis extends in a direction transverse to thefeeding direction of the hose. The rotation of the axis 24 is controlledby a central unit (not shown) in such a way that the circumferentialspeed of the heating means 23 corresponds to the feeding speed of thehose 23. The heating means 23 will then accompany the hose during apredetermined period of time. During said predetermined period of timethe heating means 23 will cut the hose 10 into sections and at the sametime seal side edges of said sections to form the bags. In theembodiment shown two bags are produced in each cycle. In one embodimentthe heating plate will engage the hose sections for cutting and sealing.Also other combined cutting and sealing means, such as radiating means,for instance laser, can be used in other applications.

The cut of bags having opposed open ends and sealed side edges are fedfrom the first conveyer 22 to the lines 14, 18 by, respectively, bydriving shafts 25, 26 which are disposed at an adjustable distance fromthe clamping roller 21. Preferably, the driving shafts 25, 26 rotate ata speed higher than the speed of the first conveyer 22. In this way thebags leaving the first conveyer will be accelerated and ride on anairflow towards a fixed stop 31. The airflow can be produced by aseparate suction nozzle or by the fixed stop 31 comprising or formingsuch a nozzle.

The lines 14, 18 comprise second and third conveyers 29, 30,respectively, the upper side of said conveyers positioned just below theoutfeed level of the driving shafts 25, 26. The fixed stop 31 at the farend of the conveyers 29, 30 as seen from the driving shafts 25, 26ensures that the bags enter the conveyers 29, 30 properly.

Second and third conveyers 29, 30 are driven in opposite directions fromthe extended centre line of the first conveyer 22 at such a speed that abag leaving the driving shafts 25, 26 will be disposed over and partlyoverlapping a bag previously taken action to. In a preferred embodimentsecond and third conveyers 29, 30 are suction conveyers. The lines 14,18 continue after second and third conveyers 29, 30 with first andsecond suction conveyers 27, 28, respectively, arranged above second andthird conveyers 29, 30. A suction conveyer can be a perforated conveyorbelt pressurised to a lower pressure on one side.

The bags are fed by second and third conveyers 29, 30 and then pulledtherefrom and lifted by first and second suction conveyers 27, 28. Ascan be seen from FIG. 3 the width of first and second suction conveyers27, 28 is lower than the width of second and third conveyers 29, 30, andlongitudinal side edges of the bags fed by first and second suctionconveyers 27, 28 will be suspended therefrom over a plate 39 (see FIG.5).

Said side edges of the bags will be folded down by first set of rollers32, towards the centre of line 14 by second set of rollers 33 andpressed towards the underside of the plate 39 by third set of rollers34. The bags then are rolled into rolls guided by clamp rollers 35engaging the underside of first and second suction conveyers 27, 28. Thefunction of the set of rollers is described more in detail below withreference to FIG. 5.

FIG. 4 shows a preferred embodiment used for feeding bags from the firstconveyer 22 to second and third conveyers 29, 30. During this passagebags 36 are preferably made “stiffer” to facilitate the transfer. Firstand second driving shafts 25, 26 are formed with first sections 37 andsecond sections 38. The diameter of said second sections 38 is smallerthan the diameter of said first sections 37. As a result the bags willbe waved to get a higher flexural rigidity in a direction perpendicularto the feeding direction. Preferably the centre distances of the drivingshafts 25, 26 can be adjusted. Another method of facilitating thetransfer of bags is to provide the bags with a an electric charge toforce the bags to repel each other. Such a method is appropriate whenthin bags are processed.

FIG. 5 shows the folding procedure of the bags. The width of the plate39 determines the width of the folded line 14. The first set of rollers32 will ensure that side edges of the bags in the line 14 are foldedcorrectly in a downward direction. Then the second set of rollers 33will fold the bags towards the centre of line 14 below the plate 39.Finally, the third set of rollers 34 will press said side edges towardsthe underside of the plate 39. Preferably all sets of rollers areadjustable and rotated by a speed higher than the feeding speed of theline 14, so as to bring forward projecting flaps or ends of the bags.

Preferably the velocity of each of the conveyers and suction conveyersis individually adjustable as well as the time period between thecutting and sealing process of the heating means 23. As a resultdifferently sized bags can be produced. The width of the plate 39 isadjustable or exchangeable.

FIG. 6 shows a roll 17 comprising a line 42 of bags. A first outer bag40 is completely rolled out of the roll 17 while a second inner bag 41only partly is rolled out. Said first bag 40 overlaps said second bag 41in an overlapping section 43. The first outer bag 40 is disposed underthe second bag 41 and covers the bottom surface of the second bag 41.Furthermore, side edges 44, 45 of the first bag 40 are folded togetherwith corresponding side edges of the second bag 41 towards a centre axisrunning in the longitudinal direction of the line 42 of bags. In thisway the first bag 40 partly encloses the second bag 41. A centralsection adjacent to the centre axis lacks in the shown embodiment afolded part.

In some applications it is appropriate to fold only one side edge 44 ofthe first bag over the corresponding side edge of the second bag 41. Theextension of the folded section varies to a large extent depending onthe application and the type of material used. Bags having a mutuallyhigher friction should require a more narrow folded section than baghaving a lower friction. In the latter case it may even be appropriateto fold side edges of the first bag right up to the centre axis. It isalso possible to fold the side edges even further to make the foldedsections overlap.

In FIG. 7 the forces acting on a roll 17 of bags 40, 41 disposed in abox 46 are shown. An outer bag 40 is shown just before releasing thesecond bag 41. Since the outer bag 40 encloses the subsequent bag 41 noflaps extend from the line or roll of bags and prevents the pull out ofbags. Two surfaces of friction doubles the friction forces to 2·μ·m·g, μbeing the friction coefficient between surfaces of plastic materials. Tomake the roll rotate in the box 46 three surfaces are operating andgenerate a total friction force of 3·μ·m·g.

When the outer bag 40 no longer encloses the second bag 41 there is nolonger a normal force and consequently no friction. The pulled out bagis then released from the subsequent bag, and there is a braking forceof μ·m·g acting on the roll. Here p can be the coefficient of frictionbetween plastic surfaces or between a plastic surface and the surface ofthe box. The latter friction should be lower than the first so as toavoid that bags are rolled out within the bag. The pull out of bags willalso be facilitated. A further advantage is that it is not necessary touse a bobbin which will facilitate the automatic winding of rolls.

The force required to pull out a bag is determined by the weight of theroll and therefore the size of the rolls is limited. It is alsodesirable to use smooth bags to form a smooth roll. Preferably thelength of the overlapping section is larger than half the circumferenceof the roll, otherwise the subsequent bag will tend to stay within thebox 46. The length of a bag should preferably be larger than thecircumference of the roll, so as to keep the roll together.

At least during the use the box 46 has to be formed with an opening 47,the length and width thereof chosen to prevent a small roll from leavingthe box 46 if a bag is pulled out quickly. This may otherwise happen atthe end of a roll. However, at that stage the each bag forms severalturns around the roll which will make it more difficult to pull out thebag. Preferably the opening 47 is shaped to facilitate the catch hold ofa bag.

What is claimed is:
 1. A method of producing plastic bags from aflattened flexible hose (10) including the steps of feeding the hose(10) in a longitudinal direction at a first speed, separating the hose(10) into bags (13) and feeding the bags (13) in a first line of bags,transferring bags of said first line of bags (13) to a second line(14,18) of bags, arranging bags (13) in said second line (14,18) of bagspartly overlapping in the longitudinal direction of the second line(14,18) of bags, folding at least one longitudinally extending side edge(15,16) of said second line (14,18) of bags, and winding said secondline (14,18) of bags to form rolls (17) of bags.
 2. A method accordingto claim 1, including the step of feeding said second line (14, 18) ofbags at a speed lower than said first speed.
 3. A method according toclaim 1, including the step of directing a first bag to form the centreof the roll (17).
 4. A method according to claim 1, including the stepof forming bags in first line into wave shape in a plane perpendicularto the plane of the flattened surface of the hose (10) and to thefeeding direction of the hose (10).
 5. A method according to claim 1,including the steps of splitting up the hose (10) into at least twolongitudinally extending sections, repeatedly separating elements (11,12) from each of said longitudinally extending sections, each element(11, 12) forming a bag, and by directing separated elements (11, 12)forming bags (13) into two lines (14, 18) fed in opposite directions. 6.A method according to claim 5, including the step of winding bags in thelines (14, 18) to form rolls (17) of bags, a first bag forming thecentre of the roll (17).
 7. A method according to claim 6, including thestep of disposing each successive bag to overlap on the outside theprevious bag in the roll (17).
 8. A method according to claim 6,including the step of disposing each successive bag on top of a bag (13)previously disposed in each of the lines (14,18).
 9. A method accordingto claim 5, including the step of folding in longitudinally extendingside edges (15, 16) of bags in said lines (14, 18) before winding lines(14, 18) into the rolls (17).
 10. A method according to claim 1, alsoincluding the steps of a) feeding each line (14) by a first suctionconveyor (27; 28) over a plate (39), b) folding longitudinally extendingopposite side edges of the line (14) down from the first suctionconveyor (27; 28) by a first set of rollers (32), c) folding in saidside edges towards the centre of the line (14) below the plate (39) by asecond set of rollers (33), and d) pressing said side edges towards theunderside of the plate (39) by a third set of rollers (34).
 11. A methodaccording to claim 10, including the step of rotating first, second andthird sets (32, 33, 34) of rollers at a speed higher than the feedingspeed of the first suction conveyor (27; 28).
 12. A method according toclaim 1, characterised by rotating heating means (23) around an axisextending transverse to the feeding direction of the hose (10), thecircumferential speed of the heating means (23) corresponding to thefeeding speed of the hose (10), so as to allow the heating means (23) toaccompany the hose during a predetermined period of time, and bycutting, during said period of time, the hose (10) into said sectionsand sealing side edges of said sections to form the bags.
 13. A devicefor producing plastic bags from a flattened flexible hose (10) includingfirst conveyer (22) for feeding the hose (10), and means for separatinghose (10) into bags running in a first line, characterised in that atleast a second conveyer (29,30) is provided for feeding the bags in afeeding direction of a second line (14,18), that means (25,26) arearranged for transferring the bags from said first conveyer (22) to saidsecond conveyer (29,30), so that the bags are overlapping in the feedingdirection of the second line (14,18) and extending in a first plane,that means (32,33,34) are arranged for folding second line (14,18)transverse to said feeding direction of the second line (14,18), andthat means (35) are arranged for winding second line (14,18) into rolls(17) of bags.
 14. A device according to claim 13, wherein the heatingmeans (23) comprises at least one heating element extending over thewidth of the flattened hose (10), and the heating element of saidheating means (23) is designed to engage the hose (10) for cutting andsealing.
 15. A device according to claim 13, wherein first suctionconveyers (27,28) are provided to engage bags of said second lines(14,18), a plate (39) is provided below said first suction conveyers(27,28), a first set of rollers (32) is provided for foldinglongitudinally extending opposite side edges of the line (14) down fromfirst suction conveyers (27,28), a second set of rollers (33) isprovided for folding in said side edges towards the centre of the line(14) below the plate (39), and a third set of rollers (34) is providedfor pressing said side edges towards the underside of the plate (39).16. A device according to claim 13, wherein said means (25,26) fortransferring the bags from said first conveyer (22) to said secondconveyer (29,30) are formed to fold bags in said first line into waveshape in a plane perpendicular to the plane of the feeding direction ofthe second line (14,18).
 17. A device according to claim 15, wherein afirst cutting means (19) is provided to cut the hose (10) into at leasttwo longitudinally extending sections, second cutting and sealing means(23) are provided to rotate around an axis extending transverse to thefeeding direction of the hose (10), the circumferential speed of thecutting and sealing means (23) corresponding to the feeding speed of thehose (10) at least during a predetermined period of time, so as to allowthe cutting and sealing means (23) to accompany the hose during saidpredetermined period of time, and to cut, during said period of time,the hose (10) into said sections and seal side edges of said sections toform the bags.
 18. A device according to claim 16, wherein the firstconveyer (22) is provided for feeding the hose (10) in a substantiallyhorizontal plane at a first horizontal level, and said at least secondconveyer (29, 30) extends in a substantially horizontal plane at asecond lower horizontal level.
 19. A device according to claim 16,wherein a third conveyer (30) is arranged to feed bags in an oppositedirection from the feeding direction of the second conveyer (29).
 20. Amethod of producing plastic bags from a flattened flexible hose (10)including the steps of feeding the hose (10) in a longitudinal directionat a first speed, separating the hose (10) into bags (13) and feedingthe bags (13) in a first line, transferring bags of said first line ofbags (13) to a second line (14,18) of bags, arranging bags (13) in saidsecond line (14,18) partly overlapping in the longitudinal direction ofline (14,18), folding at least one longitudinally extending side edge(15,16) of said lines (14,18), winding said lines (14,18) to form rolls(17) of bags and disposing the rolls one by one into a box having anopening for pulling out bags.
 21. A device for producing plastic bagsfrom a flattened flexible hose (10) including first conveyer (22) forfeeding the hose (10), and means for separating hose (10) into bagsrunning in a first line, wherein at least a second conveyer (29,30) isprovided for feeding the bags in a feeding direction of a second line(14,18), means (25,26) are arranged for transferring the bags from saidfirst conveyer (22) to said second conveyer (29,30), so that the bagsare overlapping in the feeding direction of the second line (14,18) andextending in a first plane, means (32,33,34) are arranged for foldingsecond line (14,18) transverse to said feeding direction of the secondline (14,18), means (35) are arranged for winding second line (14,18)into rolls (17) of bags, first suction conveyers (27,28) are provided toengage bags of said second lines (14,18), a plate (39) is provided belowsaid first suction conveyers (27,28), a first set of rollers (32) isprovided for folding longitudinally extending opposite side edges of theline (14) down from first suction conveyers (27,28), a second set ofrollers (33) is provided for folding in said side edges towards thecentre of the line (14) below the plate (39), and a third set of rollers(34) is provided for pressing said side edges towards the underside ofthe plate (39).
 22. A method of producing bags from a flattened flexiblehose (10) including the steps of feeding the hose (10) in a longitudinaldirection at a first speed, separating the hose (10) in a manner to forma pair of bags (13) and feeding the pair of bags (13) in a first line,transferring bags of said first line of bags (13) to a second line (14)of bags operable at a second speed, arranging bags (13) in said secondline (14) of bags partly overlapping in the longitudinal direction ofthe second line (14) of bags, folding at least one longitudinallyextending side edge (15, 16) of said second line (14) of bags, andwinding said second line (14) of bags to form rolls (17) of bags.
 23. Amethod of producing a roll of separated overlapping bags comprisingfeeding a flattened flexible hose in one longitudinal direction,longitudinally separating the flattened flexible hose into twolongitudinally extending sections, transversely separating and sealingthe longitudinally extending sections to form opposing separated opentop bags, feeding the separated bags formed from at least one of the twolongitudinally extending sections in another longitudinal direction,overlapping at least some of the separated bags being fed,longitudinally folding the overlapped separated bags being fed in theother longitudinal direction, and rolling the overlapped and folded bagsinto a roll whereby the separated bags can be withdrawn from the roll atleast one at a time.